[FFmpeg-user] "showwaves has an unconnected output" when sending audio with waveform as video

[Zoltan Kerenyi Nagy]

Hi,

I'd like to send the analog audio as video with waveform superimposed, I
did this so far:

ffmpeg -f alsa -i hw:0,0 -f lavfi -i nullsrc -filter_complex
"[0:a]showwaves=mode=line:s=hd480:colors=Red[v]" -map "[v]" -map 0:a
-pix_fmt yuv420p -b:a 360k -r:a 44100 http://localhost:5554/video.ffm

/etc/ffserver.conf

HTTPPort 5554
HTTPBindAddress 0.0.0.0
MaxHTTPConnections 10
MaxClients 10
MaxBandwidth 1024
CustomLog -

<Feed video.ffm>
    File /tmp/video.ffm
    FileMaxSize 2048M
</Feed>

#####################

<Stream video>
    Format flv
    Feed video.ffm
    VideoCodec libx264
    VideoFrameRate 15
    VideoBitRate 512
    VideoSize 1280x720
    AVOptionVideo crf 23
    AVOptionVideo preset medium
    AVOptionVideo flags +global_header

    AudioCodec aac
    Strict -2
    AudioBitRate 128
    AudioChannels 2
    AudioSampleRate 44100
    AVOptionAudio flags +global_header
</Stream>

The error message is:

Filter showwaves has an unconnected output
Tue Jan 29 22:18:08 2019 127.0.0.1 - - [POST] "/video.ffm HTTP/1.1" 200 0


------------------
(program exited with code: 1)
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